Production of concentrated acetic acid from dilute aqueous solutions of the same



1'March 15,1927. 1,621,441

` 11H PRODUCTION lOF CONCENTRATED lAC'ETIC ACID FROM DILUTE y 4 AQUEOUS SOLUTIQNS 0F THE SAME Y, r y Filed Feb.27, 1925 2 sheets-sheet 1 fr/22mm Juin@ @f ame-y,

'Marh15,19 27. DA 1,621,441

H. SUI PRODUCTION OF CONCENTRATED ACETIC ACID FROM 'DILUTE AQUEOUS SOLUTIONS 0F THE SAME Filed Feb 27. 1925 2 Sheets-Sheet a Nils/nier' amd stealm Famed Mar. 1s, 1921.

UNITED STATES 1,621,441 PATENT OFFICE.

HERMANN SUIDA, OF MODLING, LOWER AUSTRIA, AUSTRIA.

PRODUCTION or coNcEN'rRATED' ACE-TIC .ACID FROM DILUTE AQUEOUS SOLUTIONS OF THE SAME.

i A Application tiled February 27, 1925, Serial No. 12,180, and in Austria March 8, 1924.

This invention relates to the production of concentrated acetic acid from dilute aqueous solutions of the same.

It is known that acetic acid can be ex- 5 tracted, fairly satisfactorily, 'by treating dilute aqueous solutions of acetic acid with liquid solvents which, whilev insoluble or only sparingly soluble in water, have a high solvent power for acetic acid, and that, after the solvent has been suitably separated, the

\ acetic acid is more concentrated, in\respect of water, than it was originally. Accordinor to this invention the extraction of acetic acld from dilute aqueous solutions of the same can be eiected very muchmore favorably and with incomparably greater success if the mixturev of acetic acid and water vapor, from which the acetic acid. is to be extracted, is superheated to 150 C., for example, prior to treatment with solvents which have already been proposed by me for the same purpose. The solvents are those which, while being only slightly soluble or soluble to an' insignificant extent in water land having a'high solvent power for acetic acid, have la boiling point of over 150' C., that is to say, -a` boiling point considerably higher than that of pureacetic acid. Chief among these solvents .may be mentioned aromatic compounds containing hydroxyl groups and `therefore mainly bodies belongmg to the phenol group, or mixtures of the same, such asmonovalent phenols (with 4the exception of carbolic acld), for example cresols, polyvalent phenols, especially in Athe form of their ethers (guaiacol and its homologues), hydrogenized phenols, such as hexahydrocresols andv derivatives of the above mentioned compounds; and fiually all natural or artificial mixtures containing the aforesaid compounds, especially heavy phenolie'wood-tar oils (creosotes), brown-coadtar creosotes and coal tar creosotes, also liquid fatty acids having boiling points above 150 C., such as the higherhomologues of acetic acid, or also oleic acid'.

The process may be carried into Ieffect as follows:

Either a reviously superheated mixture of acetic acid and water vapor is introduced from below into the extraction apparatus (which ma suitably take the form of a column stili) while the extraction agent is introduced from the opposite direction, in counter-current, in which case the water ample, of 10% strength, is passed vapor freed from acetic acid, is discharged from the upper end of the column, while the extraction agent, saturated with concentrated acetic acid, issues from the lower end of the column. Or the process may be carried out by heating the'column'to temperatures sufficient to superheat the acetic acid with water vapor therein, without the latter being introduced in a superheated condition into the lower end of the column. f

It is well known that saturated vapors behave differently from superheated vapors. In the present instance the solvent takes up .far larger quantities of concentrated acetic acid in proportion to its own weight than it would ifV the. extraction were effected by vapors that had not been superheated. At the same time, the acetic acid contained in the extraction agent is in a far more highly concentrated state than ifthe extraction were effected, withfthe same extraction agents, from a cold or Warm liquid mixture of acetic acid and water, orfrom the mixture of the saturated acetic acid and water vapors.- This needs no explanation, since i". the extraction agent is insignificant, v

whereas the,Y solubility ofthe superheated a :etic acid vapors is very considerable. ing to the diminution-in vapor pressure, wlich is caused in the acetic acid in the presence of the extraction agent, its boiling point is considerably increased, and therefore raised above 119 C,v whereas, at'this. temperature, the water vapor, superheated to least 118 C.l or more is able to escape in the absence of any diminution in vapor pressuredue to the presence of the extraction agent.` The extraction and enrichmentprocess therefore takes place at temperatures from 101 C. upward, that is to say, above "the temperature of the -saturated mixture of acetic acid and water `vapor (assuming this to be dilute acetic acid of about 10% strength) subjected to the process.

In the accompanying drawing Figs. 1 and 2 illustrate, by way of example, diagrammatically and in partial longitudinal sec- 'tion, embodiments of devices which `will serve for carrying the process into effect.

Referring to Fig.. 1, acetic acid for exthrough a pipe 1 into a still 2, and is vaporized by means of a coil 3. The vapors pass through the pipe'..4 into a column 5, c argedv with filling material such as rings or the like, said column i being traversed by an axial heating` tube 6. Crude cresol, approximately equal in quantity to the introduced mixture of acetic acid `and water vapor, is admitted in a continuous flow through the pipe 7. Heated air is led through the heating tube 6 from below, so that the temperature of the column, at the upper end, is not much higher than 100o C., whereas, lower down, the temperature is appropriately higher, so that the vapors entering through the end of the pipe 4 which admitsthe mlxture of acetic acid and water vapor, are superheated at that point. At the lower end of the columns, hot cresol charged with acetic acid of 80 to 90% strength, is discharged continuously through the siphon 8,7and can be separated, also in a continuous manner, lnto its two components, crude cresol and hlghly Aconcentrated acetic acid (from 80 to 90% strength) in an attached still, preferably in vacuo. The water vapor escapes through the pipe 11 at the upper end ofthe column.

In another embodiment of the column apparatus, shown in Fig. 3, the column, instead of being heated by air flowlng through 'a heating tube, may be provided with several (for instance 3) heating coils 14, into which the heating Huid, which may be hot water or steam, is introduced by means of pipes 13 branching off from a main pipe 1 2. Each pipel 13 is provided wlth a regulatlngvalve 17 which makes1 it possible to mamtam the desired temperature in the coils. At the upper end of the coils the steam escapes through tubes 15 and is carried oli' through the common pipe 16. This arrangement. allows a very accurate control of the superheating temperature.

The heating of the column can also be eflfected by a heating jacket.

Ifthe operation be carried on in the same manner, ubut without superheating the va.

pors, the cresol discharged from the column will be charged with acetic acid of only 30% strength. I

Fig. 2 shows an embodiment of the column apparatus in which the mixture of acetic acid and Water vapor, of about 10% strength, is superheated prior to its admission into the column. In this case, the vapor mixture from the still 2 is rst passed through a coil 9 arranged in a vessel 10 filled with. a suitable heating liquid, andV passes thence, in a superheated condition, into the column 5, through the filling material upon which crude cresol or the like is allowed to trickle down from a pipe 7 terminating in a sprinkler 12. In this case also, the water vapor escapes through the pipe 11, while a solution of 80-90% acetic acid in cresol is discharged continuously through the Siphon 8. The heating of the column in this case is effected by the superheated mixture of acetic acid and water vapor.

In the above examples, only crude cresol is mentioned as solvent for the acetic-acid.

It is, however, self-evident that the other previously mentioned liquids could equally well be used,fwithout any alteration in the l,

working method or in the apparatus.

IVhat I claim is: l

1. A process for producing concentrated acetic acid from dilute aqueous solutions which consists in evaporating the aqueous solution, in super-heating the mixture 0f vapours of acetic acid and Water and in extracting the acetic acid from the superheated mixture.

2. A process for producing concentrated i 'acetic acid from dilute aqueous solutions thereof which consists in evaporating said solutions, in superheating the mixture -of vapours of acetic acid and waterand in extracting the acetic acid vapors from the mixture by a solvent having a higher boiling point than acetic acid.

3. A process for producing concentrated acetic acid" from dilute aqueous solutions thereof which consists in evaporating said solutions, in superheating the mixture of'- ture by 'a solvent having a higher boiling point than acetic acid, being practically insoluble in Water, and in recovering the solvent containing acetic acid.

5. A process for producing concentrated acetic acid from dilute aqueous solutions thereof which consists in evaporating said solutions, in superheating the mixture of vapours of acetic acid and water, in extract- .ing the acetic acid vapors from the mixture acetic acid, being practically insoluble in water, in recovering the solvents containing acetic acid and in separating acetic acid therefrom by distillation.

7. A process for producing concentrated acetic acid from dilute aqueous solutions thereof which'consists in evaporating said solutions, in superheating the mixture of vapours of acetic acid and water, in extracting the acetic acid vapors from the mixture by cresol, in recovering the cresol and in separating acetic acid therefrom by distillation. Y

8. A process for producing concentrated acetic acid from dilute aqueous solutions thereof which consists in evaporating said solutions, in superheatin vapours of acetic acid an water during extraction and within the extraction ap aratus, in extracting the acetic acidvapors rom the mixture by a solvent having a higher boiling point than acetic acid, being practically in- 20 soluble in water, and in recovering the solvent containing acetic acld.

In testimony whereof I- aflix my signature. i

HERMANN SUIDA.

the lmixture of l5 

